In molecular biology, G-quadruplexes (also known as G-tetrads or G4-DNA) are nucleic acid sequences that are rich in guanine and capable of forming a four-stranded structure (Shampay, J., Szostak, J. W., Blackburn, E. H. DNA sequences of telomeres maintained in yeast. Nature 310, 154-157). Four guanine bases associate through Hoogsteen hydrogen bonding to form a square planar structure called a guanine tetrad, and two or more guanine tetrads can stack on top of each other to form a G-quadruplex. They can be formed of DNA (Blackburn, E. H. Structure and function of telomeres. Nature 350, 569-573, 1991, Simonsson T. G-Quadruplex DNA Structures—Variations on a Theme Biol. Chem. 382, 621-628, 2001, Wang, K. Y., McCurdy, S., Shea, R. G., Swaminathan, S., Bolton, P. H. A DNA aptamer which binds to and inhibits thrombin exhibits a new structural motif for DNA. Biochemistry 32, 1899-904 1993) or RNA (Joachimi, A., Benz, A., Hartig, J. S. “A comparison of DNA and RNA quadruplex structures and stabilities”. Bioorg. Med. Chem. 17, 6811-6815 (2009)) and may be intramolecular, bimolecular, or tetramolecular. Depending on the direction of the strands or parts of a strand that form the tetrads, structures are described as parallel or antiparallel. The G-quadruplex structures as telomeres at the chromosomal ends are meant for conservation of genetic information during repeating cell cycles and are also capable of specific interactions with proteins. DNA is a molecule that encodes the genetic instructions used in the development and functioning of all known living organisms and many viruses. In nature, DNA is based on 2′-deoxyribose and has its phosphate links between carbons 3′ and 5′ of adjacent nucleosides. It is however observed that 3′-deoxyribose is not a good basis for nucleosides to carry genetic information as a isoDNA. A stable duplex in DNA with mixed sequences is required, and 3′-deoxyribose in 2′-5′ linked isoDNA does not form stable duplexes. isoDNA is studied in the art to achieve better stability of duplexes. The 3′-deoxy-2′-5′-linked isoDNA sequences are known to form duplexes with complementary RNA. However their thermal stability is lower compared to the DNA:DNA/DNA:RNA or RNA:RNA duplexes known in the art. One important structure often observed within single stranded G-rich DNA aptamers is the G-quadruplex. No such example exists in literature till today that the G-rich isoDNA can form a G-quadruplex structure. Szostak et. al in ‘Functional RNAs exhibit tolerance for non-heritable 2′-5′ versus 3′-5′ backbone heterogeneity’; Nature—Chemistry 5, 390-394 (2013) discloses synthetic mixed-backbone RNA aptamers with randomly interspersed 2′-5′ and 3′-5′ phosphodiester linkages compatible for folding into defined three-dimensional structures such as stem-loop structure that retain molecular recognition with 10%-25% tolerance to 2′-5′ doping heterogeneity in a 3′-5′ backbone. However, Szostak et al provide a mixture of randomly interspersed 2′-5′ and 3′-5′ phosphodiester linkages in the backbone of RNA aptamers and do not provide RNA or DNA aptamers with solely 2′-5′ phosphodiester linkages. Thrombin binding aptamer (TBA) is a SELEX derived aptamer sequence 5′-G1G2T3T4G5G6T7G8T9G10G11T12T13G14G15-3′. Backbone modifications of TBA are reported to have profound effects on the structural topology of the tetraplex formed. The folding patterns of an isosequential TBA RNA sequence showed that in contrast to the unimolecular antiparallel G-quadruplex structure of TBA (FIG. 2) (Wang, K. Y., McCurdy, S., Shea, R. G., Swaminathan, S., Bolton, P. H. A DNA aptamer which binds to and inhibits thrombin exhibits a new structural motif for DNA. Biochemistry 32, 1899-904, 1993). the RNA-TBA oligomer formed a multimolecular parallel G-quadruplex (FIG. 2). A mixed DNA/RNA backbone TBA sequence, depending on the position of the ribo- or deoxyribo-nucleotides in the sequence, either folded in DNA-like or RNA-like quadruplex structures. RNA-based SELEX against thrombin gave a completely different nucleobase sequence compared to DNA-TBA. The recently discovered 3′-2′-TNA (FIG. 1) aptamer against thrombin was G-rich sequence but not the same as TBA. The loop configuration of the quadruplex also can be the deciding factor of various structural topologies with varying loop configurations. It is evident from this discussion that the backbone element is the crucial governing entity for maintaining the functional structural quadruplex topology of any given sequence. Avino A et al in Bioorg Med Chem. 2012 Jul. 15; 20(14):4186-93, report the synthesis of modified thrombin-binding aptamers (TBAs) carrying uridine (U), 2′-deoxy-2′-fluorouridine (FU) and North-methanocarbathymidine (NT) residues in the loop regions. Replacement of thymidine in TGT loop by U and FU results in an increased stability of the antiparallel quadruplex structure of TBA. However, synthesis of 2′-5′ linked isoDNA TBA comprising substitution of T by U in the TGT loop for anti-thrombin activity is not provided by Avino et al. In light of the above, there remains a need in the art to provide isoDNA oligomers that are capable of forming G-quadruplex structures which will be able to maintain biological molecular recognition and functional ability. Further, the evaluation of structural topology and stability of G-quadruplexes formed by isoDNA as functional molecule for use in therapeutics and diagnostics applications is of importance and relevance, which remain the objects of the invention.